This invention relates generally to prosthetic knee joints for use by above-the-knee amputees. More particularly, this invention relates to prosthetic knee joints which simulate the motion of a natural knee.
In the past it has been common to employ simple pin joints in prosthetic knees. Simple pin joints, however, are inherently unstable in a standing posture unless the joint is provided with a stop means. Frequently, simple pin joints have a toggle action to provide a stop which gives the required stability. Such toggle actions, however, generally require an abnormally high force to cause initial flexion between femoral and tibial portions of a prosthetic leg. Moreover, simple pin joints result in a poor dynamic simulation of a human knee which has a very complex sliding and rolling motion between the femur and the tibia. Another problem with simple pin prosthetic knee joints is that they are difficult to brake effectively in a natural manner.
Another approach to the construction of a prosthetic knee joint has been the use of a polycentric joint. Typically such polycentric prosthetic knee joints comprise one or more links interconnecting a femoral member and a tibial member. The polycentric knee joints are generally quite complex. Moreover, the polycentric knee joints are also vulnerable to wear in addition to being noisy in use, even during simple ordinary walking. An additional disadvantage is that the multiple links are generally heavy and are susceptible to accidental damage.
A third construction for known prosthetic knee joints is the condylar knee joint. The condylar knee joints are characterized by articulable members which are provided condyles (i.e., articular prominences) that resemble the condyles of human femoral and tibial bones. Conventionally, the condylar surface of the femoral member and condylar surface of a tibial member are in contact such that there is constant rubbing friction therebetween during flexure between the femoral and tibial members. This constant friction presents an inherent disadvantage in such condylar knee joints: an amputee using the knee joint must continually exert energy to operate the knee joint unless there is some means of reducing the friction. Moreover, the friction between the tibial condyles and the femoral condyles results in a rapid wear of the rubbing surfaces. While lubrication may be used to eliminate the rapid wear, a messy knee joint results that is not well adapted to use in a prosthetic knee. Another disadvantage of conventional condylar knee joints is instability during a standing posture. Yet another disadvantage is that the condylar surfaces are frequently fabricated of materials which make the knee joint susceptible to accidental damage.
A common problem with previously known prosthetic knee joints is the inability to accommodate torsional motion between femoral and tibial portions of the joint which typically results during each step of normal walking and even more when one is following a curved path.
Recognizing the need for an improved prosthetic knee joint, it would therefore be desirable to provide a quiet, modular knee joint having a dynamic behavior, knee trajectory and load bearing capability which effectively simulates those characteristics in a natural knee joint.
In addition, it would be desirable to have a prosthetic knee joint which is not highly vulnerable to wear or accidental damage and which does not require lubrication.
An additional desirable feature for a prosthetic knee joint would be the provision of brake apparatus which resists the flexure of the knee joint with a force moment that increases with flexure of the knee joint and which provides shock absorbency for the prosthetic knee joint.
It would also be desirable to provide a prosthetic knee joint which will accommodate relative rotation between a natural hip joint and a foot such as that rotation which occurs when a normal individual is walking.
Another desirable feature of a prosthetic knee joint would be the incorporation of an extension aid which would facilitate the extension of the knee joint toward an unflexed position.